This application responds to NIH program announcement PAR-99-031 (NCRR shared instrumentation grant) and requests funding to purchase a replacement transmission electron microscope for the Department of Obstetrics and Gynecology, Yale University School of Medicine. For the last three decades, under NIH support, the reproductive neuroscience group in our department has been studying basic central and peripheral mechanisms that underlie normal reproduction and pathological conditions, primarily using morphological methods. We have also been collaborating with other departments. The transmission electron microscope is used for funded projects in the department (80%) plus collaborative projects (20%). The 12 projects listed in the application use ultrastructural analyses by transmission electron microscopy. Through a similar NIH initiative, we purchased a Philips CM 10 electron microscope 15 years ago. The Department has paid for the construction and maintenance of the electron microscopic suite and supporting facilities during this period, and will continue to do so. Although there are other electron microscopes in other departments of the Medical School and the University, because all the projects of the PI and those of Drs. Csaba Leranth and Tamas Horvath utilize electron microscopy as a primary tool of investigation our group has the need for the equipment almost every hour of the working day and on weekends. Thus, it is impossible to resolve our need of an electron microscope on a shared basis with other departments. Through this initiative, we are applying to purchase a new electron microscope: Our 15 year old Philips CM 10 transmission electron microscope contributed observations that have been published in hundreds of peer reviewed research articles, but it is now completely broken and out of service. The heavy use of the machine resulted in increasing numbers of breakdowns during the past year. Because this model has been long discontinued, it is difficult to find the appropriate replacement parts to rebuild the microscope. It has been abandoned as a viable instrument and we are temporarily using a "mothballed" obsolete machine. But, this one cannot withstand the load and will soon break down for good. Twelve government-supported projects are listed (see text) that in the aggregate require constant use of an electron microscope. Without the possibility of purchasing a new electron microscope, these projects are in jeopardy! It is the conclusion of all participants that the most user-friendly and durable microscope currently available is the Philips Tecnai 10, which is the model that replaced the popular Philips CM 100 model. We describe the Philips Tecnai 10 in the text. We are requesting funds urgently to purchase this machine and an image analysis package in order to support our NIH-funded projects.